There are known arts in which an ant groove having a trapezoidal sectional shape is utilized as a sealing structure in a sealed place required to have airtightness.
The ant groove structure has a merit such that the fitted sealing material little falls off. The ant groove structure is assumed to be a structure suitable for such as gate valves which repeat their opening and closing.
There are proposed various arts of improving the shape or structure of the sealing material in order to enhance performances such as airtightness as to the above sealing structure which utilizes the ant groove.
Patent document 1 proposes a sealing material for an ant groove wherein the sealing material is approximately in the shape of a teardrop such that a larger arched portion and a smaller arched portion are connected together through a straight edge. The fitting is facilitated by pressing first the smaller arched portion of the sealing material into the ant groove. In a fitted state, it is assumed that: one straight edge contacts with a bottom face of the ant groove, and the smaller arched portion fits into an inner corner at one side of the ant groove, and another straight edge contacts with an inner sloping face of the ant groove, whereby the sealing material is disposed in a stable state, so that there occurs little twisting.
Patent document 2 relating to a patent application previously made by the applicant of the present patent application discloses a sealing material for an ant groove wherein the sealing material comprises: circular-arc-shaped projecting portions which project in three directions; and concave inlet portions, each of which is located between the projecting portions. When fitted to the ant groove, this sealing material for an ant groove can be passed comparatively easily through a narrow opening of the ant groove by pressing the opposite circular-arc-shaped projecting portion side of the sealing material into the ant groove, with one concave inlet portion of the sealing material as the base point in a state where this concave inlet portion is disposed on an opening edge of the ant groove. In a state where the sealing material is fitted to the ant groove, a pair of circular-arc-shaped projecting portions disposed in a bilaterally symmetrical shape contact with the bottom face of the ant groove and, in the center, the remaining one circular-arc-shaped projecting portion contacts with a member facing the ant groove, whereby the good elastic deformation or sealing function can be performed.
[Patent Document 1]                JP-A-510286/1997 (Kohyo)        
[Patent Document 2]                JP-A-130481/2002 (Kokai)        
The aforementioned prior arts also have problems such that: the fitting to the ant groove is difficult to carry out, or the falling off from the ant groove tends to occur.
In the art of the patent document 1, after the teardrop-shaped sealing material for an ant groove has been inserted into the ant groove with the smaller arched portion of the sealing material down, the smaller arched portion must be pressed into the inner corner at one side of the ant groove in a way that the entirety of the sealing material is twisted. The motion of properly twisting the entirety of the sealing material for the ant groove in the narrow ant groove is difficult, and the fitting has directionality. Therefore, misfitting tends to be caused. From above the ant groove, it cannot be checked whether the smaller arched portion has surely be disposed into the inner corner at one side or not. Thus, there is a worry that the use is made with the fitting left insufficient. In addition, the occupation ratio of the sealing material to the ant groove is so small that, in the case where compressed repeatedly, the sealing material repeats its contact with the inner wall surface of the ant groove and therefore tends to generate particles due to friction.
As to the art of the patent document 2, the fitting to the ant groove is easier than that of the teardrop-shaped sealing material of the patent document 1. However, the motion of gyratorily pressing the opposite circular-arc-shaped projecting portion side into the ant groove, with the aforementioned concave inlet portion as the base point, needs great force. Its reason can be considered to be that, unless the entirety of the circular-arc-shaped projecting portion is elastically deformed, the sealing material cannot be passed through the opening of the ant groove. When an attempt is made to release the sealing made with the sealing material for an ant groove, such as when a motion of opening a gate valve is made, there occurs a phenomenon such that the sealing material for an ant groove unfavorably slips out of the ant groove in the form of having attached to the opposite member. This fixation phenomenon is a phenomenon which greatly occurs between a sealing material (e.g. rubber) and a metal member when the sealing material is applied to such as a gate valve of a semiconductor production apparatus, to the sealed place of which a fixation-preventing means such as greasing or coating cannot be applied. The concave inlet portions, which are disposed in positions bilaterally symmetrical as to the concave inlet portion that is utilized as the base point during the fitting, do not take part in the fitting function. Therefore, there is a possibility that the elastic repulsive force or sealing function of the sealing material for an ant groove may be spoiled correspondingly to the presence of the concave inlet portions in three places.